The biggest difference between the bottom dual coil in old version and the newest bottom dual coil is the wick in the coil.
Wicks in upgraded coil are all wrapped inside the coil, this makes the coil more hygienic.

Overall I get great results from these bottom dual coils. I have 5 - 6 tanks that I refill 2 X's daily each. So Yeah I vape non-stop. I replace all 1 X/week. So I average using a package of coils a week total. And I like the 1.8 ohm. These work well with my p** through batteries as well as my other batteries, even the Twist batteries. Every once in a while I get a dud in the package that won't vape at all. But for the price & because I order frequently & quite a few it's not that big of a deal. However, for that reason I can only give it a 4 star rating.

I'm now on coil number 3 of my first ever pack, and I'm absolutely loving these coils. I am using them in an Aerotank mini and if you see my review for that device I noted that, that is the best device I have ever used. The Aerotank came equipped with two of almost the exact same coils heads, however the ones that came in my kit had one large hole on each side instead of two small holes like these ones. Unfortunately my first coil (the one that came with the Aerotank) began to gurgle after the second day. Since then I have primarily used these as replacements. I also tried one of the original coils - that I purchased as back up because of the terrible reviews these coils received here. I have to say that contrary to the reviews here these coils out perform the old ones by far!!! The old coils are OK however they produce less vapor and don't taste nearly as good.
So far I seem to be able to run about 20mls through each coil head before their performance begins to drop. At which point I replace them. I haven't tried cleaning them because I think that for the price it is unnecessary. After 20 odd mls I have not yet had any issue with clogging or a burnt taste; just reduced vapor and flavor, apart from the first stock coil that started gurgling after a day ~ as I mentioned. I'm using a few different e-liquids but the primary liquids I am using are from The Mad Alchemist (TMA) and are a 70/30 VG/PG blend. the other liquids I am using are dekang's T- Blend and Joyetech's clear spring. These liquids are probably a 70/30 PG/VG blend. None of which have any issue wicking or building up and burning.
So far I am VERY happy! If they lasted a bit longer I would give them five stars but at 20 odd mls a piece they are still good value for money. They also produce ridiculous amounts of vapour and taste fantastic :)
A+

I'm now on coil number 3 of my first ever pack, and I'm absolutely loving these coils. I am using them in an Aerotank mini and if you see my review for that device I noted that, that is the best device I have ever used. The Aerotank came equipped with two of almost the exact same coils heads, however the ones that came in my kit had one large hole on each side instead of two small holes like these ones. Unfortunately my first coil (the one that came with the Aerotank) began to gurgle after the second day. Since then I have primarily used these as replacements. I also tried one of the original coils - that I purchased as back up because of the terrible reviews these coils received here. I have to say that contrary to the reviews here these coils out perform the old ones by far!!! The old coils are OK however they produce less vapor and don't taste nearly as good.
So far I seem to be able to run about 20mls through each coil head before their performance begins to drop. At which point I replace them. I haven't tried cleaning them because I think that for the price it is unnecessary. After 20 odd mls I have not yet had any issue with clogging or a burnt taste; just reduced vapor and flavor, apart from the first stock coil that started gurgling after a day ~ as I mentioned. I'm using a few different e-liquids but the primary liquids I am using are from The Mad Alchemist (TMA) and are a 70/30 VG/PG blend. the other liquids I am using are dekang's T- Blend and Joyetech's clear spring. These liquids are probably a 70/30 PG/VG blend. None of which have any issue wicking or building up and burning.
So far I am VERY happy! If they lasted a bit longer I would give them five stars but at 20 odd mls a piece they are still good value for money. They also produce ridiculous amounts of vapour and taste fantastic :)
A+

Work great for two or three days, then inlets turn black and plug up so little vapor. Better count on having a large supply of them available. I'm going to try and see if they can be cleaned with an ultrasonic cleaner to give them a longer life.